#include <iostream>
#include <string>

class User {
private:
    std::string username;
    std::string password;
    std::string email;

public:
    User(std::string username, std::string password, std::string email = "") {
        this->username = username;
        this->password = password;
        this->email = email;
    }

    void displayInfo() {
        std::cout << "Username: " << username << ", Password: " << password << ", Email: " << (email.empty() ? "Not provided" : email) << std::endl;
    }
};

int main() {
    User user1("Alice", "password123", "alice@example.com");
    User user2("Bob", "password456");

    user1.displayInfo();
    user2.displayInfo();

    return 0;
}
